When wishing to obtain layers with varying doping, so-called trench technology has hitherto been employed. However, this technology suffers from unavoidable disadvantages since trenches can economically be formed only to a depth of a few .mu.m, because it relies on relatively low etching rates for etching the trenches. Etched trenches have very steep side walls and tend to assume a curved shape when a high lateral etching rate is used. This may possibly lead to gaps in the epitaxial layer. Overall, with the conventional process, the production costs are relatively high and the yield leaves much to be desired.
Epitaxial layers with laterally varying doping are, for example, needed for the production of high-voltage MOSFETS, as are described in DE 43 09 764 C2. In this known high-voltage MOSFET, in an inner zone within a space-charge zone that extends in the event of a high threshold voltage, additional zones of conductivity type opposite to that of the inner zone are arranged so that regions with respectively opposite conductivity types alternate with one another in the lateral direction. By virtue of these additional zones, it is possible to provide the MOSFET with a low bulk resistance in the conducting region, even though it has a high threshold voltage.
Satisfactory production of an epitaxial layer with laterally varying doping, that is to say an epitaxial layer in which, for example, p-type conductivity regions and n-type conductivity regions alternate with one another laterally, has not yet satisfactorily been achieved.
It is desirable to have a process for producing an epitaxial layer with lateral varying doping. It is also useful that the angle of inclination of the interfaces between the differently doped regions of the epitaxial layer be controlled.